Beloved, you do not need to worry about how it will be fulfilled. That's God's portion. He has promised it and He will bring it to fulfillment.
And not being weak in faith, he did not consider his own body…he did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, and being fully convinced that what He had promised He was also able to perform.
(Romans 4:19-21, NKJV)
We can learn from Abraham. He wasn't concerned whether his body was old or his wife was way past age. All Abraham was concerned about is that God who promised is willing and able to do it.
Therefore, do not look around, neither should you look at yourself. But, focus on Him who said it and is able to perform it.
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